This is the 6013th most frequent French word.
double
Twice; twofold.
Here, 'double' describes the locking mechanism having two locks, emphasizing enhanced security.
Je préfère les clés à double serrure pour plus de sécurité.
I prefer double-lock keys for more security.
In this example, 'double' quantifies the amount, indicating twice the usual quantity.
Nous avons commandé une portion double de dessert.
We ordered a double portion of dessert.
Here, 'double' illustrates the feature of the mirror having two usable sides.